1. Field of Invention
The present invention relates generally to semiconductor processing equipment. More particularly, the present invention relates to a caster which isolates a reaction frame from an active vibration isolation system on which a stage apparatus is situated, while still enabling the stage apparatus, the active vibration isolation system, and the reaction frame to be moved as a unit.
2. Description of the Related Art
For precision instruments such as photolithography machines which are used in semiconductor processing, factors which affect the performance, e.g., accuracy, of the precision instrument generally must be dealt with and, insofar as possible, eliminated. When the performance of a precision instrument is adversely affected, as for example by reaction forces or by vibrations, products formed using the precision instrument may be improperly formed and, hence, defective. For instance, a photolithography machine which is subjected to vibratory motion may cause an image projected by the photolithography machine to move, and, as a result, be aligned incorrectly on a projection surface such as a semiconductor wafer surface.
Scanning stages such as wafer scanning stages and reticle scanning stages are often used in semiconductor fabrication processes, and may be included in various photolithography and exposure apparatuses. Wafer scanning stages are generally used to position a semiconductor wafer such that portions of the wafer may be exposed as appropriate for masking or etching. Reticle scanning stages are generally used to accurately position a reticle or reticles for exposure over the semiconductor wafer. Patterns are generally resident on a reticle, which effectively serves as a mask or a negative for a wafer. When a reticle is positioned over a wafer as desired, a beam of light or a relatively broad beam of electrons may be collimated through a reduction lens, and provided to the reticle on which a thin metal pattern is placed. Portions of a light beam, for example, may be absorbed by the reticle while other portions pass through the reticle and are focused onto the wafer.
A stage such as a wafer scanning stage or a reticle scanning stage is typically supported by a base structure such that the stage may move in a linear direction. Planar or linear motors may be used to facilitate the movement of wafer scanning stages and reticle scanning stages within a photolithography apparatus or an exposure apparatus. A motor which moves or drives a stage is often mounted between the stage and the base structure. When a motor causes a stage to move, forces are typically created between moving and non-moving portions of the motor, and reaction forces are also generally created. That is, forces which accelerate the stage also act on the base structure substantially equally, and in the opposite direction. Such reaction forces may cause the base structure to move, and may also cause vibrations to be induced in the base structure. Movement of the base structure renders it more difficult to position the stage, as motion of the base structure causes the stage to move.
As will be appreciated by those skilled in the art, forces or vibrations generated within a photolithography apparatus or exposure apparatus may cause issues relating to photolithography and exposure operations. The accuracy associated with such operations may be compromised when forces and vibrations affect the positioning of wafers or reticles, for example. To reduce the effect of reaction forces and vibrations which may be induced by the reaction forces associated with moving a stage assembly, reaction frames are often used to substantially isolate the reaction forces and to direct the reaction forces away from the stage assembly, e.g., to a ground surface. In addition to using reaction frames, an active vibration isolation system (AVIS) may be used to reduce the effect of vibrations within the overall photolithography apparatus. Often, reaction frames and base structures may be mounted on a caster which facilitates positioning of an overall apparatus that includes the reaction frames and the base structures.
FIGS. 1a and 1b are diagrammatic representations of an apparatus which includes a caster. An apparatus 102 includes a stage assembly 106, which may include components that are sensitive to vibrations, that is supported on an AVIS 110. Stage assembly 106 is coupled to a reaction frame 114 which is arranged to absorb reaction forces associated with moving a stage included in stage assembly 106. Both AVIS 110 and reaction frame 114 are supported on a caster 118. Caster 118, which may be positioned on legs 122, is generally used to enable apparatus 102, or a machine, to be readily moved between different locations. In other words, apparatus 102 may be moved as a substantially cohesive unit using caster 118, as AVIS 110 and reaction frame 114 are both mounted on caster 118.
Although caster 118 is often formed from a material such as polymer concrete which is typically effective to absorb vibrations and reaction forces associated with reaction frame 114, some vibrations modes may be transmitted from reaction frame 114 to AVIS 110 through caster 118. In addition, some vibrations or forces associated with reaction frame 114 may cause movement of caster 118. Any movement of caster 118 may give rise to performance issues in stage assembly 106. As such, photolithography or exposure processes associated with apparatus 102 may be compromised.
Therefore, what is needed is a caster which enables an apparatus positioned thereon to be moved as a unit, while reducing the transmissions of reaction forces or vibrations through the caster. That is, what is desired is an isolated caster system which enables an apparatus positioned thereon to be moved as a unit, while allowing reaction forces and vibrations to be isolated and prevented from affecting vibration-sensitive portions of the apparatus.
The present invention relates to reducing the coupling of vibrations within a caster system which facilitates overall positioning of an apparatus supported on the caster system. According to one aspect of the present invention, a caster system that supports portions of a stage apparatus, which has a reaction frame and a stage assembly, includes a first caster component and at least a second caster component. The first caster component supports the stage assembly, while the second caster component supports the reaction frame and is vibrationally separated from the first caster component. The second caster component may be physically coupled to the first caster component to enable the first caster component, the second caster component, the reaction frame, and the stage assembly to be moved as a substantially single unit. In one embodiment, the first and second caster components are arranged to be physically separated when the stage apparatus is not being moved.
A caster system which includes an isolated frame caster enables vibrations which may be induced within a reaction frame to be passed to the isolated frame caster, while substantially not affecting the portion of the caster system that supports an active vibration isolation system. Enabling vibrations to be isolated prevents a stage assembly supported on the active vibration isolation system from being affected by vibrations or movement caused by the vibrations. Further, allowing the isolated frame caster to be physically coupled to other portions of the isolated frame caster when the reaction frame and the active vibration isolation system is moved facilitates the movement of the reaction frame and the active vibration isolation system.
According to another aspect of the present invention, a caster system that facilitates movement of a substantially attached stage apparatus which has a stage assembly and a reaction frame includes a first component to which the stage assembly is coupled and a second component to which the reaction frame is coupled. The second component is vibrationally isolated from the first component to prevent at least one vibrational mode associated with the reaction frame from causing an affect in the first component. The first component and the second component are further arranged to be physically coupleable to facilitate the movement of the stage apparatus.
In one embodiment, the second component and the first component are arranged to be physically coupled using at least one bracket mechanism to enable the first component, the second component, the reaction frame, and the stage assembly to be moved as a substantially single unit. In another embodiment, the second component and the first component are arranged to be physically coupled using a first material to enable the first component, the second component, the reaction frame, and the stage assembly to be moved as a substantially single unit. In such an embodiment, the first material may be a soft rubber material.
According to another aspect of the present invention, an apparatus includes a stage assembly, a reaction frame, and a caster system. The stage assembly includes a table, and a motor that is arranged to cause the table to move and generates a reaction force when the table moves. The reaction frame is coupled to the stage assembly, and the reaction force is arranged to be transmitted from the motor to the reaction frame. The caster system includes a first caster component that is arranged to support the stage assembly and a second caster component that is arranged to support the reaction frame. The caster system facilitates the stage assembly and the reaction frame as a substantially single unit. The second caster component is arranged to be physically coupled to the first caster component and vibrationally isolated from the first caster component.
These and other advantages of the present invention will become apparent upon reading the following detailed descriptions and studying the various figures of the drawings.